Method and apparatus for monitoring and processing component carriers

ABSTRACT

A method and apparatus are described which perform bandwidth aggregation by simultaneously monitoring and processing a number of simultaneous, non-contiguous or contiguous component carriers in the downlink. A wireless transmit/receive unit (WTRU) can be configured by an evolved Node-B (eNodeB) to support additional component carriers. A pre-configured additional component carrier may be used. Various methods for activating and deactivating the additional component carrier are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/578,673, filed Oct. 14, 2009, which claims the benefit of U.S.Provisional Application No. 61/110,209, filed Oct. 31, 2008, which isincorporated by reference as if fully set forth.

TECHNICAL FIELD

This application is related to wireless communications.

BACKGROUND

A key feature of long term evolution advanced (LTE-A) is a higher datarate. This is supported by allowing a wireless transmit/receive unit(WTRU) to receive and transmit data on multiple LTE component carrierssimultaneously in both uplink and downlink. This is referred to ascarrier aggregation.

Receiving and transmitting on multiple carriers significantly increasesthe power consumption of the WTRU. It is known that the powerconsumption of the analog front-end, (which counts as a significantfraction of total power consumption at the WTRU), is linearlyproportional to the bandwidth or a plurality of basic frequency blocks(i.e., component carriers) that are aggregated. Activating anddeactivating additional component carriers on demand and rapidly iscritical to saving WTRU resources, (e.g., hybrid automatic repeatrequest (HARQ) processing (including channel quality indicator (CQI) andsounding reference signal (SRS) reporting), buffer occupancy and buffermanagement, (e.g., buffer status report (BSR) reporting) and schedulingprocessing), and providing savings of power consumption.

SUMMARY

A method and apparatus are described which perform bandwidth aggregationby simultaneously monitoring and processing a number of simultaneous,non-contiguous or contiguous component carriers in the downlink. A WTRUcan be configured by an evolved Node-B (eNodeB) to support additionalcomponent carriers. A pre-configured additional component carrier may beused. Various methods for activating and deactivating the additionalcomponent carrier are also described.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows a wireless communication system including an eNodeB and aWTRU;

FIG. 2 is a block diagram of the eNodeB of FIG. 1;

FIG. 3 is a block diagram of the WTRU of FIG. 1; and

FIGS. 4 and 5 show procedures for monitoring and processing componentcarriers.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment.

When referred to hereafter, the terminology “evolved Node-B (eNodeB)”includes but is not limited to a base station, a site controller, anaccess point (AP), or any other type of interfacing device capable ofoperating in a wireless environment.

FIG. 1 shows a wireless communication system 100 including an eNodeB 105and a WTRU 110. The eNodeB 105 is configured to transmit a radioresource control (RRC) connection reconfiguration message 115 to theWTRU 110.

Various methods and apparatus for activating or deactivating thereception or transmission on the different carriers in an advanced LTEsystem employing carrier aggregation are described.

Transition to Connected Mode

In an idle mode, the WTRU 110 monitors and processes only a singlecomponent carrier. Idle mode procedures, such as system information (SI)acquisition and paging indication (PI) monitoring are transparent to themultiple carrier capability of the WTRU 110. Schemes like cell selectionand cell reselection may remain the same with or without carrieraggregation, (referred to as bandwidth aggregation hereinafter),capability or may consider the bandwidth aggregation capability of theinfrastructure, (eNodeB 105), as an input to system selection. However,as the WTRU 110 transitions to an RRC connected mode, (typically throughan RRC connection request), the network is informed by the WTRU 110 ofthe WTRU capability in terms of bandwidth aggregation.

WTRU bandwidth aggregation capability can be defined as the number ofsimultaneous non-contiguous component carriers that can be monitored andprocessed simultaneously in the downlink for each band. An alternativemetric can be the number of radio frequency (RF) receivers, (withdifferent receivers handling non-contiguous carriers), and the largestbandwidth of each receiver. Consider an example where there are fivecomponent carriers: carriers 1 and 2 are contiguous to each other butnot to carriers 3, 4 and 5, and carriers 3, 4, and 5 are contiguous.

WTRU bandwidth aggregation capability can also be defined as the numberof simultaneous contiguous carriers that can be monitored and processedsimultaneously in the downlink for each band.

WTRU bandwidth aggregation capability can also be defined as the largestsupported bandwidth of aggregated contiguous carriers, not only thenumber of carriers, but also bandwidth.

WTRU bandwidth aggregation capability can also be defined as the largesttotal bandwidth of aggregated carriers (contiguous or not).

WTRU bandwidth aggregation capability can also be defined as the largestbandwidth supported per single carrier (in line with LTE current WTRUcapability).

RRC Configuration of Component Carriers

After the WTRU informs the network of the WTRU's bandwidth capability inthe RRC connection procedure, an eNodeB supporting bandwidth aggregationmay configure the WTRU to support additional component carriers, (i.e.,pre-configured additional component carriers). This may be performedwith an RRC connection reconfiguration message carrying information thatallows the WTRU to set up the monitoring, (grants and assignments), ofone or more additional downlink and/or uplink carriers. Informationincluded in the RRC connection reconfiguration message may include thecell identity (ID), the carrier center frequency, the carrier bandwidth,the carrier direction (uplink or downlink), and other informationrequired to setup in a timely fashion the activation and synchronizationof pre-configured additional component carriers.

One RRC connection reconfiguration message may be sufficient to setupmore than one component carrier by stacking the information previouslydescribed for all pre-configured additional component carriers.

The reception of the RRC connection reconfiguration message alone maynot activate the monitoring and processing of the additional componentcarriers immediately or after a delay. In this case, only an explicit orimplicit activation command as described below would allow the WTRU tostart monitoring and processing additional carriers. Alternatively, theRRC connection reconfiguration message may contain a field that signalswhether or not the monitoring and processing should start after thesuccessful reconfiguration procedure is completed. This may be useful toverify at setup that the pre-configured additional component carriersare operational. Alternatively, the reception of the RRC connectionreconfiguration message activates the monitoring and processing of theadditional component carriers immediately or after a delay.

The RRC connection reconfiguration message may contain the additionalinformation that would allow the WTRU to setup additional componentcarriers controlled by another eNodeB, such as timing advance and othersynchronization related information.

The RRC connection reconfiguration message can provide a specific cellradio network temporary identifier (C-RNTI) per additional componentcarrier.

The RRC connection reconfiguration message may, for efficiency, assignto each pre-configured additional component carrier a bit combination upto the number of maximum simultaneous additional component carriers thatcan be supported, so that activation or deactivation of an individualcomponent carrier can be referred to by using this assigned bitcombination.

Mechanisms to Activate or Deactivate Pre-Configured Additional ComponentCarriers

MAC Control Elements

Activation or deactivation of a pre-configured additional carrier or apre-defined subset of pre-configured additional carriers can occur atthe reception of a medium access control (MAC) control element (CE). Theactivation or deactivation can take effect after a predefined delay,(fixed or configurable through higher layer signaling), or immediatelyafter reception of the MAC CE. This would be implemented by a new typeMAC CE, referred to as a MAC_CE_Activation control element.

The MAC_CE_Activation control element may contain a bit combinationfield to indicate which pre-configured carrier is being activated ordeactivated. Alternatively, the carrier being activated or deactivatedmay be indicated by the C-RNTI value used for the transmission of theMAC PDU containing the MAC control element. One MAC_CE_Activationcontrol element may activate or deactivate multiple carriers at the sametime by aggregating the bit combinations or transmitting multiple MACPDUs using a different C-RNTI.

The indication of whether the command corresponds to activation ordeactivation may be performed by setting a bit or it may be implicitbased on the current activation or deactivation state of the carrier.Alternatively, it may be based on the carrier the MAC PDU was receivedon. For example, if the MAC CE was contained in a MAC PDU received in agiven carrier, (e.g., an “anchor carrier” or a “serving cell”), then thecommand is understood to be for activation of the carrier indicated inthe MAC CE. If the MAC CE was contained in a MAC PDU received in acarrier, (possibly without explicit indication of a carrier within theMAC CE itself), then the command is understood to be a deactivation forthe carrier the MAC PDU was received from, or alternatively adeactivation for a pre-defined set of carriers.

Another alternative is that all MAC_CE_Activations are always receivedon a specific carrier, (e.g., the carrier corresponding to the servingcell).

Activation on Demand

The reception of a physical downlink control channel (PDCCH) on aspecific carrier (such as an “anchor carrier”) with a new downlinkcontrol information (DCI) format (or a modified DCI format for LTEadvanced) may signal to the WTRU that transmission to, or receptionfrom, a pre-configured additional uplink (PUSCH) or downlink (PDSCH)carrier, (or a pre-defined subset of pre-configured additional uplink ordownlink carriers), will take place in X subframes. (To start monitoringthe PDCCH on a new carrier requires a few subframes of lead time.) Thedelay allows the WTRU analog front-end to setup to the new carrier,which includes phase-locked loop (PLL) and automatic gain control (AGC)settling time and frequency synchronization. The new DCI format containsa field to map the activation with the pre-configured carrier asexplained above. This allows the WTRU to only monitor the PDCCH from asingle carrier, (e.g., a special carrier called “anchor carrier” or thecarrier corresponding to the serving cell), and consequent batterysavings. The indication from the anchor carrier may be for a singlegrant or assignment on the additional component carrier. In this case,HARQ feedback corresponding to the grant or assignment may also bedelayed (with respect to the PDCCH transmission) compared to existingsystems. Alternatively, the indication from the anchor carrier maysignal to the WTRU that it should start monitoring the PDCCH on theadditional component carrier or subset of component carriers until thiscarrier (or these carriers) is (are) deactivated.

The PDCCH received with a new DCI format (or modified DCI format for LTEadvanced) on a carrier, (e.g., an “anchor carrier”), may provide a timedelayed allocation (physical resource blocks (PRBs), modulation andcoding sets (MCS), and the like) on a pre-configured additionalcomponent carrier. The delay is based on the WTRU capability to tune andsynchronize to a pre-configured component carrier. This delay may befixed or variable based on WTRU capability. Time delayed allocation isalready used for uplink allocation—a four subframe delay. However, thismethod allows the WTRU to know about the possibility of an upcominguplink transmission more in advanced compared to the existing system.Such advance knowledge may be useful for uplink scheduling decisions.The same approach may be used for a pre-configured additional componentcarrier. This brings the advantage that pre-configured additionalcomponent carriers are activated on demand by allocating the resourcesin advance.

Implicit Activation

Implicit activation of one or a number of carriers may take place whenthe volume of traffic received on the downlink, (measured at thePhysical (PHY), MAC, radio link control (RLC), or packet dataconvergence protocol (PDCP) layer), within a pre-determined orconfigured amount of time exceeds a pre-determined or configuredthreshold. There may be several thresholds defined, each correspondingto a particular carrier to activate. For example, carrier C1 may beactivated when the volume of traffic exceeds V1, and carrier C2 may beactivated when the volume of traffic exceeds V2, and the like.

Implicit activation of one or a number of carriers may also take placewhen the WTRU initiates transmission, (either on the random accesschannel (RACH), physical uplink control channel (PUCCH), or physicaluplink shared channel (PUSCH)), on a certain uplink carrier that isassociated to the downlink carrier to activate. This association may bepre-defined or provided to the WTRU through RRC signaling, (systeminformation or dedicated signaling).

When a downlink carrier is activated, the WTRU initiates reception onthe PDCCH configured for this carrier, (if a PDCCH is defined percarrier), and transmission on the PUCCH is configured for this carrierto transmit the feedback information.

Implicit Deactivation

Implicit deactivation may be performed based on an inactivity timerspecific to the additional component carrier activity. For example, onlythe anchor carrier is active during a Web browsing session. If adownload is started, start allocating PRBs on the pre-configuredadditional component carrier for this WTRU. Once the download iscompleted, the network stops assigning resources to the pre-configuredadditional component carrier for the WTRU. After some inactivity timer,(specific to the pre-configured carrier), expires, the WTRU stopsmonitoring the PDCCH, (i.e., dedicated PDCCH per carrier), and shutsdown the front-end radio resources allocated to this carrier.Alternatively, the WTRU may stop monitoring the PDCCH of a carrier afterexpiry of a timing alignment timer (or other timer) defined specificallyfor this carrier. Such a timing alignment timer may be restarted basedon the reception of a timing alignment MAC control element from a MACPDU received on the carrier.

In the case of activation on demand and a shared control channel on theanchor carrier, the WTRU can shut down the front-end resources allocatedto a pre-configured additional component carrier as soon as the timedelayed allocation to this carrier is not received. The WTRU maydetermine that it is more optimal to wait for a few consecutivesubframes without allocation to pre-configured additional componentcarriers before shutting down the front-end resources associated withthese carriers.

Implicit deactivation may also be based on radio conditions. As anexample, if the channel conditions of a carrier remain under a certainminimum threshold for a period of time, the front-end radio resourcesmay be de-allocated.

Explicit Deactivation Order on PDCCH

Explicit deactivation may be performed by sending a deactivation orderspecific to the component carrier so that the WTRU no longer needs tomonitor the PDCCH, (dedicated PDCCH per carrier). The order may be sentusing a PDCCH with a new DCI format on the anchor carrier for thededicated channel. Alternatively, the deactivation order using the PDCCHmay be sent only to the pre-configured additional component carrier.

Activation or Deactivation in DRX Connected Mode

MAC DRX configuration may remain the same with carrier aggregation.On-duration and DRX cycle apply to the configured carriers, (e.g., an“anchor carrier” or serving cell), as well as to activatedpre-configured additional component carriers, (“resource carriers”).

A DRX_Inactivity_timer running in the WTRU may be started or restartedif the PDCCH is received over an activated pre-configured additionalcomponent carrier for a new transmission.

The DRX_Inactivity_timer may also be started or restarted if a scheduledgrant for an activated pre-configured additional component carrier isreceived for a new transmission.

Alternatively, the MAC DRX configuration may have a specificDRX_Inactivity_timer for each of the pre-configured additional componentcarriers. The DRX_Inactivity_timer associated to a carrier would bestarted or restarted when a PDCCH assignment is received on thiscarrier. This would enable the WTRU to effectively deactivate thesepre-configured carriers until the next on-duration cycle while theanchor carrier remains in active time.

The logic described previously for the DRX_Inactivity_Timer may alsoapply to other DRX timers, such as the ON_Duration_Timer and theDRX_Retransmission_Timer.

FIG. 2 is a block diagram of the eNodeB 105 of FIG. 1. The eNodeB 105includes an antenna 205, a receiver 210, a processor 215 and atransmitter 220. The receiver 210 is configured to receive a signalindicating a bandwidth aggregation capability of the WTRU 110. Thetransmitter 220 is configured to transmit an RRC connectionreconfiguration message to the WTRU 110.

FIG. 3 is a block diagram of the WTRU 110 of FIG. 1. The WTRU 110includes an antenna 305, a receiver 310, a processor 315, a transmitter320 and a discontinuous reception (DRX) inactivity timer 325.

The WTRU 110 monitors and processes component carriers. The receiver 310in the WTRU 110 is configured to monitor and process a single componentcarrier. The transmitter 320 in the WTRU 110 is configured to transmit asignal indicating a bandwidth aggregation capability of the WTRU 110.The receiver 310 is further configured to receive an RRC connectionreconfiguration message. The processor 315 in the WTRU 110 is configuredto set up for monitoring and processing at least one pre-configuredadditional component carrier.

The receiver 310 may be further configured to receive a MAC CE, and theprocessor 315 may be configured to activate or deactivate thepre-configured additional component carrier.

The pre-configured additional component carrier may be immediatelyactivated or deactivated in response to receiving the MAC CE, or may beactivated or deactivated after a predefined delay. The pre-configuredadditional component carrier may be an uplink carrier or a downlinkcarrier.

The WTRU 110 may monitor and process the single component carrier whilein an idle mode.

In one example, the bandwidth aggregation capability may indicate anumber of simultaneous non-contiguous component carriers that can bemonitored and processed simultaneously in the downlink for each band.

In another example, the bandwidth aggregation capability may indicate anumber of RF receivers and the largest bandwidth of each receiver.

In yet another example, the bandwidth aggregation capability mayindicate a number of simultaneous contiguous carriers that can bemonitored and processed simultaneously in the downlink for each band.

In yet another example, the bandwidth aggregation capability mayindicate the largest supported bandwidth of aggregated contiguouscarriers.

In yet another example, the bandwidth aggregation capability mayindicate the largest total bandwidth of aggregated carriers.

In yet another example, the bandwidth aggregation capability mayindicate the largest bandwidth supported per single carrier.

The bandwidth aggregation capability may indicate more than one of theexamples described above.

In another scenario, the receiver 310 may be configured to receive aPDCCH on a specific carrier with a DCI format that indicates thattransmission to, or reception from, a pre-configured additional uplinkor downlink carrier will take place in a certain number of subframes.The processor 315 may be configured to set up for monitoring andprocessing the pre-configured carrier.

FIG. 4 shows a procedure 400 for monitoring and processing componentcarriers. In step 405, a WTRU monitors and processes a single componentcarrier. In step 410, the WTRU transmits a signal indicating a bandwidthaggregation capability of the WTRU. In step 415, the WTRU receives anRRC connection reconfiguration message. In step 420, the WTRU sets upfor monitoring and processing at least one pre-configured additionalcomponent carrier. In step 425, the WTRU activates or deactivates thepre-configured additional component carrier in response to receiving aMAC CE.

FIG. 5 shows a procedure 500 for monitoring and processing componentcarriers. In step 505, a WTRU monitors and processes a single componentcarrier. In step 510, the WTRU receives a PDCCH on a specific carrierwith a DCI format that indicates that transmission to, or receptionfrom, a pre-configured additional uplink or downlink carrier will takeplace in a certain number of subframes. In step 515, the WTRU sets upfor monitoring and processing the pre-configured carrier.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, application specific integrated circuits (ASICs),application specific standard products (ASSPs), field programmable gatearrays (FPGAs) circuits, any other type of integrated circuit (IC),and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, mobility managemententity (MME) or evolved packet core (EPC), or any host computer. TheWTRU may be used in conjunction with modules, implemented in hardwareand/or software including a software defined radio (SDR), and othercomponents such as a camera, a video camera module, a videophone, aspeakerphone, a vibration device, a speaker, a microphone, a televisiontransceiver, a hands free headset, a keyboard, a Bluetooth® module, afrequency modulated (FM) radio unit, a near field communication (NFC)module, a liquid crystal display (LCD) display unit, an organiclight-emitting diode (OLED) display unit, a digital music player, amedia player, a video game player module, an Internet browser, and/orany wireless local area network (WLAN) or ultra wide band (UWB) module.

What is claimed is:
 1. A method implemented by a wireless transmit/receive unit (WTRU), the method comprising: receiving a radio resource control (RRC) reconfiguration message, wherein the RRC reconfiguration message configures the WTRU to support at least one additional component carrier and the RRC reconfiguration message does not activate the at least one additional component carrier; receiving a medium access control (MAC) control element (CE), wherein the MAC CE indicates that the at least one additional component carrier is to be activated, and the MAC CE comprises a bit combination field that is indicative of which component carriers are to be activated; and activating the at least one additional component carrier based on receiving the MAC CE.
 2. The method as in claim 1, wherein activating the at least one additional component carrier comprises beginning to process transmissions sent via the at least one additional component carrier.
 3. The method as in claim 2, wherein the at least one additional component carrier is activated after a predefined delay after receiving the MAC CE.
 4. The method as in claim 1, wherein the bit combination field indicates which component carriers are to be activated based on identifying information for the component carriers that is assigned in the RRC reconfiguration message.
 5. The method as in claim 1, wherein the bit combination field indicates that multiple component carriers are to be activated.
 6. The method as in claim 1, wherein the bit combination field indicates that at least one active component carrier is to be deactivated.
 7. The method as in claim 1, wherein the bit combination field comprises an aggregation of identifiers for a plurality of component carriers.
 8. The method as in claim 1, further comprising maintaining a deactivation timer for each active component carrier, wherein the WTRU stops monitoring a physical downlink control channel (PDCCH) for the active component carrier upon expiration of the deactivation timer for the active component carrier.
 9. The method as in claim 8, wherein the deactivation timer for the active component carrier is started based on resources being assigned to the WTRU on the active component carrier.
 10. The method as in claim 1, wherein the RRC reconfiguration message comprises a cell identity and a carrier frequency for the at least one additional component carrier.
 11. A wireless transmit/receive unit (WTRU) comprising: a processor and memory, the processor configured to: receive a radio resource control (RRC) reconfiguration message, wherein the RRC reconfiguration message configures the WTRU to support at least one additional component carrier and the RRC reconfiguration message does not activate the at least one additional component carrier; receive a medium access control (MAC) control element (CE), wherein the MAC CE indicates that the at least one additional component carrier is to be activated, and the MAC CE comprises a bit combination field that is indicative of which component carriers are to be activated; and activate the at least one additional component carrier based on receiving the MAC CE.
 12. The WTRU as in claim 11, wherein the processor is further configured to: start processing transmissions sent via the at least on additional component carrier upon activating the at least one additional component carrier.
 13. The WTRU as in claim 11, wherein the bit combination field indicates which component carriers are to be activated based on identifying information for the component carriers that is assigned in the RRC reconfiguration message.
 14. The WTRU as in claim 11, wherein the bit combination field indicates that multiple component carriers are to be activated.
 15. The WTRU as in claim 11, wherein the bit combination field indicates that at least one active component carrier is to be deactivated.
 16. The WTRU as in claim 11, wherein the processor is further configured to maintain a deactivation timer for each active component carrier, wherein the WTRU is configured to stop monitoring a physical downlink control channel (PDCCH) for the active component carrier upon expiration of the deactivation timer for the active component carrier.
 17. The WTRU as in claim 16, wherein the deactivation timer for the active component carrier is started based on resources being assigned to the WTRU on the active component carrier.
 18. The WTRU as in claim 11, wherein the RRC reconfiguration message comprises a cell identity and a carrier frequency for the at least one additional component carrier.
 19. The WTRU as in claim 11, wherein the processor is further configured to initiate reception of a physical downlink control channel (PDCCH) of the at least one additional component carrier after a pre-defined delay upon activating the at least one additional component carrier.
 20. An evolved Node-B (eNB) comprising: a processor and memory, the processor configured to: transmit a radio resource control (RRC) reconfiguration message, wherein the RRC reconfiguration message configures a wireless transmit receive unit (WTRU) to support at least one additional component carrier, and the RRC reconfiguration message does not activate the at least one additional component carrier for use by the WTRU; transmit a medium access control (MAC) control element (CE) to the WTRU, wherein the MAC CE indicates that the at least one additional component carrier is to be activated for use by the WTRU and the MAC CE comprises a bit combination field that is indicative of which component carriers are to be activated by the WTRU; and send at least one transmission to the WTRU via the at least one additional component carrier. 